1. Field of the Invention
This invention relates to a system and process for producing fatty acids and paraffinic wax alternatives from triglycerides derived from plants and animals. Specifically, the present invention relates to a process for cross-linking glycerol fatty acid ester-containing compositions, producing free fatty acids and separating free fatty acids from a cross-linked residue. The free fatty acids may be fractionated. The residual cross-linked ‘bottoms’ may be used as an additive to crude triglyceride prior to hydrogenation thereof. The hydrogenation of a blend of cross-linked bottoms with crude triglyceride possesses properties that render it suitable for use as a paraffinic wax substitute.
2. Background of the Invention
Oils extracted from vegetable seeds and produce such as soy, corn, rapeseed and the like consist primarily of triglycerides. Triglycerides are composed of a glycerin molecule combined with three fatty acids. The term “fatty acids” is commonly understood to refer to the carboxylic acids naturally found in animal fats, vegetable, and marine oils. The major difference between vegetable oils derived from different sources is in the fatty acid component of the triglycerides. Fatty acids can vary in the number of carbon atoms in the molecule and in the number of double bonds in the fatty acid. The majority of the fatty acids in vegetable oils have carbon numbers of from about 8 to about 20 carbons. Fatty acids with the same number of carbon atoms may have different degrees of unsaturation (different numbers of double bonds). For example, stearic acid contains no double bonds (i.e. it is saturated), while oleic acid, linoleic acid, and linolenic acid contain a single double bond, two double bonds, and three double bonds, respectively.
Fatty acids without double bonds are known as saturated fatty acids, while those with at least one double bond are known as unsaturated fatty acids. The most common saturated fatty acids are palmitic acid (16 carbons) and stearic acid (18 carbons). Oleic and linoleic acid (both containing 18 carbons) are the most common unsaturated fatty acids.
Trans fatty acids are unsaturated fatty acids that contain at least one double bond in the trans isomeric configuration. The trans double bond configuration results in a greater bond angle than the cis configuration. This results in a more extended fatty acid carbon chain more similar to that of saturated fatty acids rather than that of fatty acids comprising cis unsaturated double bonds. The conformation of the double bond(s) impacts the physical properties of a fatty acid. Fatty acids containing a trans double bond have the potential for closer packing or aligning of acyl chains, resulting in decreased mobility; hence fluidity is reduced when compared to fatty acids containing a cis double bond. Trans fatty acids are commonly produced by the partial hydrogenation of vegetable oils. Saturated fats and trans isomers of unsaturated fatty acids are undesirable as food product components, as there is some indication that they are unhealthy. Due to these health concerns with saturated fats and fats containing trans fat, low trans fat content is desirable when fats are to be consumed.
Triglycerides, also known as triacylglycerols, can by hydrolyzed to yield carboxylic acids and alcohols. Reaction products produced by the complete hydrolysis of a fat or oil molecule are one molecule of glycerol and three fatty acid molecules. This reaction proceeds via stepwise hydrolysis of the acyl groups on the glyceride, so that at any given time, the reaction mixture contains not only triglyceride, water, glycerol, and fatty acid, but also diglycerides and monoglycerides.
Fatty acids that are separated or split from the glycerine backbone of the triglyceride molecule are commonly used as is and/or as a raw material in a variety of industries including the food, cosmetics, pharmaceutical, and chemical industries.
Fatty acids may be split from the glycerine molecule by several means. Due to its favorable cost, a widely used commercial process for hydrolyzing fats and oils is a high-temperature steam treatment method known as the Colgate-Emery Steam Hydrolysis Process. This method, and modifications thereof, uses a countercurrent reaction of water and fat under high temperatures ranging from 240° C. to 315° C. and high pressures in the range of 4.93 MPa (700 psig) to 5.17 MPa (750 psig). In this method, a tower is used to mix the fat and water to increase the efficiency of the hydrolysis reaction. Typically, fat is introduced into the bottom of the tower with a high pressure feed pump. Water is introduced to the top portion of the tower at a ratio of 40%-50% of the weight of the fat. As the fat ascends though the descending water, a continuous oil-water interface is created. It is at this interface that the hydrolysis reaction occurs. Direct injection of high pressure steam raises the temperature to approximately 260° C. and the pressure is maintained at from 4.83 MPa (700 psig) to 4.93 MPa (715 psig). The increased pressure causes the boiling point of the water to increase, allowing for the use of higher temperatures, which results in the increase solubility of the water in the fat. The increased solubility of water provides for a more efficient hydrolysis reaction. This continuous, countercurrent, high pressure process allows for a split yield of 98%-99% efficiency in 2 to 3 hours. Further purification of the fatty acid product obtained by this method is often accomplished by separation, e.g. distillation.
Other methods of hydrolysis are also used to avoid by-product formation and unsaturated fat degradation which are associated with the high pressure-high temperature hydrolysis of unsaturated fats and oils. Such methods include the hydrolysis of unsaturated oils by splitting them with a base followed by acidulation or by enzymatic hydrolysis. Split yields are generally lower than that for the Colgate-Emery process under similar time conditions.
Hydrogenated vegetable oils that have been heavily hydrogenated have been used to replace petroleum waxes in such applications as candles, boxboard coatings and adhesives. Petroleum waxes in most of these applications have melting points in excess of 48° C. (120° F.). This minimum melting point is desirable in order to avoid melting of the petroleum wax in tropic or hot summer conditions or in such as applications as hot pour and seal hot melt adhesive applications.
Vegetable waxes derived from triglycerides may be hydrogenated to increase the melting point. The degree of hydrogenation is usually measured by the iodine value of the wax. Very low iodine values are required in order for the hydrogenated vegetable oil to have melting points in excess of 48° C. (120° F.). Additionally, when the melting point of a hydrogenated vegetable oil is increased it becomes harder as noted by the needle penetration value, a common test known to those experienced in the art. As the melting point and hardness of the vegetable wax increase due to additional hydrogenation, the wax becomes more brittle. Brittle waxes tend to crack on flexing and are not suitable for applications such as flexible packaging and adhesives. Use of low iodine value (IV) vegetable wax in candle applications is generally undesirable because the wax tends to crack on solidifying, which is aesthetically undesirable.
Efforts to hydrogenate triglycerides to provide for a less brittle more flexible high melting product have been reported. To overcome the deficiencies of low IV hydrogenated triglyceride wax, additives and/or diluents are typically used to modify the triglyceride wax and make it more flexible, less brittle and/or higher melting. Compounds that have been added include mono- and diglycerides, vinyl polymers, petroleum and microcrystalline waxes, styrene butadiene polymers, fatty acids, alpha olefins, and glycerin.
Some of the problems associated with prior art include undesirable burning characteristics of the additives used to impart flexibility in candle applications and the fact that conventional additives may not be renewable, leading to environmental concerns. Also the addition of additives to impart flexibility and increased melt point requires an additional mixing step that is undesirable due to the additional manufacturing involved.
Accordingly, there is still a need in the industry for a system and method of splitting fatty acids from triglycerides, thereby producing fatty acids that exhibit superior product appearance, texture, and/or stability, and to provide a method for its preparation whereby a co-product is obtained that can be utilized to enhance hydrogenation of oil. The co-product may be used to produce solid vegetable wax useful as an alternative to or admixture component with petroleum waxes.